This aspect of the program is concerned with charcterization of gonadotropin and prolactin receptors of the gonads and of the physical and functional relationships of the LH receptor site and adenylate cyclase. We have devised a procedure for purificatin of microgram quantities of active lactogen receptors from rat ovaries. The receptor is composed of two dissimilar subunits of Mr 88,000 and 40,000, the latter being probably an integral part of the larger form. Aggregation of receptor subunits and/or holereceptor has been suggested by FLPC fractionation of the free receptor in the presence of non-ionic detergents. Free receptors showed binding activity of Mrs 150,000 and 250,000, and aggregates dissociateid upon SDs/mercaptoethanol tratment into the lower molecular forms. These could represent dimeric and trimeric forms of the holoreceptror (80,000). A method for iodination of purified prolactin receptor with preservation of activity was used to corroborate the Mr/s of the free receptor and hormone-receptor complexes after crosslinking the 125-I-receptor with unlabeled hormone. Results confirmed values initially obtained by crosslinking experiments using labeled hormone and unlabeled receptor. When radiolabeled receptor was used for studies on receptor subunit aggregation, dimeric and trimeric forms were observed. Our results indicate that the detergent soluble receptor appeared to be aggregated forms of holoreceptors. The potential for aggregation of subunits and/or holoreceptors is suggested by these findings, and the mechanism by which aggregation or clustering of prolactin receptors would trigger the biological response remains to be elucidated. Chromatofocusing of free receptors showed three isoforms of pIU, 4.0 5.0 and 5.3 indicating glycoprotein and or phosphorylation heterogeneity. We have purified the LH/hCG receptor on wheat germ lectin-Sepharose and hCG Sepharose, which also allows purification of lactogen receptor from the initial starting material. The LH receptor was identified as a single protein Mr 70,000. The technique is simple and allows purification of microgram amounts of active receptor suitable for structural studies microsequencing, and functional reconstitution.